In prior art data processing systems if the user wanted to expand the memory capacity it has been the practice to add memory subsystems along a general memory bus. Generallly, such memory subsystems have been composed of many memory array modules. Each array module has been designed to interface to the bus and has its own controller circuitry for memory array signal timing generation. When such a subsystem has been subjected to alteration in size, either a new subsystem has been substituted or the array modules have been manually reconfigured to assume the proper relative position within the memory subsystem. Such reconfiguration typically involved setting switches, wire-wrapping shunt posts, and/or soldering in various types of shunts. Such practices have created installation problems and reliability problems which in the final analysis result in higher computer system costs. The present invention enables the user to readily expand or reduce the memory capacity by employing one or more universal expandable memory circuit cards.